1. Technical Field
The present invention relates to an ultrasonic sensor and a manufacturing method for the ultrasonic sensor.
2. Related Art
In the related art, there is an ultrasonic sensor that includes a piezoelectric element which transmits and/or receives an ultrasonic wave, a vibrating plate in which the piezoelectric element is provided, and an sonic adjustment layer which propagates the ultrasonic wave. For example, there is an ultrasonic sensor that includes an electromechanical conversion element (piezoelectric element), a movable film (vibrating plate), and a sonic propagation member (sonic adjustment layer) provided in an opening (space) on a side of the movable film, which is opposite to the electromechanical conversion element (see JPA-2011-255024 (claims 1 and 2, a paragraph [0054], and the like) and JP-A-2011-259274 (paragraphs [0051] and [0053], FIG. 6, and the like)).
Both the ultrasonic sensors in JP-A-2011-255024 and JP-A-2011-259274 are classified as a type (so-called CAV surface type) in which a side of the vibrating plate, which is opposite to the piezoelectric element, is an ultrasonic wave passing region. In both JP-A-2011-255024 and JP-A-2011-259274, it is proposed that a sealing member, which seals the piezoelectric element, is provided on the piezoelectric element side of the vibrating plate. A recessed portion is formed at the center of the recessed portion and the sealing member covers the peripheral region of the piezoelectric element.
However, in JP-A-2011-255024 and JP-A-2011-259274, in the case of providing the sealing member, a problem arises in that it is difficult to ensure high reliability. In other words, in a case where a plurality of piezoelectric elements are collectively arranged, an opening area of the recessed portion formed in the sealing member is increased. In this case, when predetermined pressure is applied to the vibrating plate from the sonic adjustment layer side, the vibrating plate is significantly deflected in the recessed portion of the sealing member and, as a result, there is a concern that structural distortion will occur, and thus, reliability will be decreased. Depending on cases, there is a concern that cracking will appear on the respective members. This is not a problem limited to the ultrasonic sensors disclosed in JP-A-2011-255024 and JP-A-2011-259274, but every CAV surface type ultrasonic sensor has the same problem.